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| Silverfish |
We’re not
going far today, mainly because I’ve got this wood pile to sort out and seeing
as you’re with me I thought you could give me a hand. Bit of a cheek I know but
woodpiles always turn up something interesting. Like this silverfish for
example. Just pop him in the tin and we’ll take a closer look at him. They are
pretty easy to recognise; very small insects with tapering abdomens and three
cerci pointing left, right and centre. These are the guys you see running
across your carpet at night or invading your bookshelves and they’ve been with
us since the first plants colonised the Earth some four hundred million years
ago. A bold evolutionary step, coming out of the sea like that but they’ve rather
rested on their laurels since then as they’ve remained substantially unchanged
ever since. Almost as if they are saying “We’ve done our bit – the rest is up
to you.”
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| Southern Skimmer Dragonfly |
You will
have noticed that silverfish have no wings. You have to jump forward seventy
five million years or so for that development to take place. Earth at this time
(known as the carboniferous period) was a warm and swampy place, trees were
laying down the first coal beds for us to rip up later (though I doubt that
this was their intention) and the abundance of plant life was flooding the
atmosphere with oxygen. Insects took to
the air in the form of Grasshoppers, Mayflies and Dragonflies and not just
delicate little creatures like that Southern Skimmer sunning itself on the fence
over there. All that oxygen gave the Dragonflies (or to be accurate:
Griffinflies as their forerunners are known) a chance to really stretch their
wings, all two and a half feet of them. Put your arm out for a moment and
imagine a Griffinfly sitting on the crook of your elbow. One wing tip would be
brushing your fingertips while the other one tickled your ears.
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| Cockroach nymph |
Life
continued in this heady vein with cockroaches being the dominant land insects - there goes one now. Come back it won’t bite you - it's only a youngster anyway. Anyhow, dear old
Earth passed pleasantly from the Carboniferous to the Permian period a little
under three hundred million years ago. Things were simple then: just one sea,
Panthalassa, and one continent, Pangaea, rapidly drying out as the interior was
an inconvenient distance from the sea generated cloud systems. The transition
from swamp to desert led to major developments in plant life (although flowers
were still some way in the future) and the true bugs and beetles evolved into
the basic forms we know today. And then, 252 million years ago, things suddenly
went terribly wrong.
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| Beetles survived The Great Dying 252 million years ago |
This was
the Permian-Triassic Extinction Event, often referred to as The Great Dying, when
life on Earth was substantially wiped out. The reason was sudden and due to catastrophic
climate change, the cause of which is still under investigation. Could be that
all the coal and gas laid down by the great forests got fed up with hanging
around under what was to become Siberia and exploded; possibly the warming of
the ocean caused a massive bloom of methane producing microbes; or maybe too
many volcanoes erupted in too short a time. The old favourite, meteor impact
hasn’t been ruled out either. Whatever the cause, life sustaining oxygen was in
short supply and animals on land and in the sea were asphyxiated into
extinction and this included 83% of the insect genera known to exist at the
time. The insects that we’ve already mentioned were among the lucky ones.
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| Pollinators like this Nomada Bee evolved alongside flowering plants |
Mass
extinction isn’t all bad news however. Planet Earth is home to many life forms,
including ourselves, and like all houses the occasional clear out can be very
beneficial. Think of it as a planet-wide spring clean. It took a fair few million years for the dust
to settle but it gave life, including our insect friends, a clean slate on
which to develop in new and exciting ways but it wasn’t until the Cretaceous
period (145-65 million years ago) that our story reaches its next plot
development. It was during this period when the planet settled down into the
form we now recognise, with the continents beginning to settle into place, and we
saw the evolution of flowering plants. This gave the insects a whole new food
source to exploit and the pollinators appeared on the scene, including these
pesky (but still useful) flies that keep landing on us.
The
cretaceous period ended with a bang when a large wandering rock dropped out of
space and landed on the Yucatán Peninsula in Mexico. Although this wiped out
the dinosaurs, paving the way for mammals such as ourselves to develop, all of
the insect orders survived and over the past 65 million years they have been
evolving into the families, genera and species that keep our cereals growing,
our livestock fed and our species alive. So there you have it, insect evolution
in a nutshell. Love them or loathe them we couldn’t exist without them. Well,
that’s the log pile sorted, thanks for your help. I hope I haven’t bored you
too much with all these geological time periods but sometimes it’s nice to get
a new perspective on commonplace things. Here, I’ve made you a little chart of some
of the commoner insect orders to be found on Crete (and elsewhere in the world
for that matter). You can go out and play I-Spy insects now. So what if you’re
in your fifties? It’s never stopped me.
Until
next week – happy hunting.
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LINKS:
Naturalists
(the facebook page that accompanies this blog)
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